The long term goal of this project is to better understand epithelial stem cell biology. Epithelial stem cells are responsible for the continual regeneration of self-renewing tissues such as epidermis, hair follicle, and cornea. We originally identified putative epithelial stem cells in the bulge of the hair follicle. We then isolated a keratin 15 promoter that targets bulge cells in transgenic mice. The K15 promoter allowed for the isolation, lineage analysis and molecular characterization of hair follicle stem cells. We showed, that bulge cells have properties of stem cells, and isolated bulge cells can reconstitute hair follicles, epidermis and sebaceous glands. We have now identified a number of genes which we hypothesize maintain the stem cell phenotype. In this grant application we will: 1. evaluate whether genes upregulated in the bulge cells are importantfor maintaining the hair follicle stem cell phenotype by: a. overexpressing candidate genes in non-hairfollicle stem cells of transgenic mice, and then testing whether these cells behave as hair follicle stem cells. b. blocking candidate gene pathways specifically in the bulge cells using our KlSCrePrl mice to delete or overexpress genes specifically in the bulge cells. 2. determine if genes downregulated in telogen bulge cells are involved in stem cell activation and/or lineage determination by: a. generating inducible transgenic mice in which candidate genes are over-expressed in bulge cells using an RU486 inducible system, and b. deleting candidate "bulge activation" or lineage determining genes specifically in bulge cells and their progeny using theKlSCrePRl mice. 3. develop means for isolating and characterizing human hair follicle stem cells. a. We will establish whether genes identified in mouse bulge are also expressed in human bulges. b. We will delineate hair follicle stem and progenitor cells within both the mouse and human hair follicle based on cell surface protein expression patterns. These distinct subpopulations of cells within the hair follicle will be isolated by fluorescent activated cell sorting, and their stem cell nature, gene expression patterns and functional characteristics will be discerned. Patients with alopecia, hair shaft disorders, basal cell carcinoma, hair follicle tumors, or chronic wounds could potentially benefit from this research.